1. Technical Field
The present disclosure relates to a pixel driving method. More particularly, the present disclosure relates to a pixel driving method for pixels at a high gray scale range.
2. Description of Related Art
The use of various liquid crystal display products have become commonplace in recent times. However, the conventional liquid crystal display still has the problems of a narrow viewing angle, i.e., the image is partially white when viewed at an oblique angle on both sides of the liquid crystal display, so that the screen of liquid crystal display generates a color washout situation. The conventional approach is to divide each pixel of the liquid crystal display into a red sub-pixel, green sub-pixel and blue sub-pixel, and each sub-pixel is divided into two display regions. Through a pixel circuit design that enables two display regions of each sub-pixel to have different pixel voltages such that the luminance of one display region is different from the luminance of another display region, the quality of the image is improved.
However, although this approach achieves white balance compensation when users watch the liquid crystal display at oblique viewing angles, if it is desired to display a high gray scale, the degree to which the luminance of the blue sub-pixel decreases is much greater than the decrease in the luminance of the red sub-pixel and green sub-pixel. Accordingly, when users watch the liquid crystal display at oblique viewing angles, the image quality is poor since the display image is partially green.
Referring to FIG. 1, FIG. 1 is a diagram illustrating a relation between gray scales and normalized luminance of a conventional red sub-pixel, green sub-pixel, and blue sub-pixel at an oblique view (45 degrees) and direct view. There are six curves L1, L2, L3, L4, L5, and L6 in FIG. 1. The curves L1, L2, and L3 represent relations between normalized luminance of the red sub-pixel, green sub-pixel, and blue sub-pixel respectively at a direct view. The curves L4, L5, and L6 represent relations between normalized luminance of the red sub-pixel, green sub-pixel, and blue sub-pixel respectively at an oblique view.
As shown in FIG. 1, when a pixel has a gray scale value larger than 192, i.e., the pixel has a gray scale value within a range A1, the curve L6 (blue sub-pixel) at an oblique view is more concave than the curve L3 at a direct view. In other words, the luminance of the blue sub-pixel at an oblique view is lower than the luminance of the blue sub-pixel at a direct view. On the other hand, the curve L4 (red sub-pixel) at oblique view is less concave than the curve L3 at a direct view. The curve L5 (green sub-pixel) at an oblique view is also less concave than the curve L2 at a direct view.
Referring to FIG. 1 and FIG. 2, FIG. 2 is a diagram illustrating a relation between normalized luminance at an oblique view (45 degrees) and normalized luminance at a direct view for a conventional red sub-pixel, green sub-pixel, and blue sub-pixel, in which the curves N1, N2, and N3represent the red sub-pixel, the green sub-pixel, and the blue sub-pixel, respectively. The reference line N4represents no color washout effect. As shown in FIG. 2, when the normalized luminance at direct view is larger than 0.7, i.e., when the pixel has a gray scale value within a range A2, the difference between the curve N3(blue sub-pixel) and the reference line N4is larger than the difference between the curve N1(red sub-pixel) and the reference line N4, and the difference between the curve N2(green sub-pixel) and the reference line N4. In other words, when the pixel has a large gray scale value, the reduction of the luminance of the blue sub-pixel is larger than the reduction of the luminance of the red sub-pixel and green sub-pixel at an oblique view (45 degrees) causing the luminance of the pixel to appear to lack blue. Therefore, when the pixel has a large gray scale value, a condition in which the image is partially green at an oblique view (45 degrees) occurs.